There are multiple ways to describe insomnia:
A brief episode of difficulty sleeping. Acute insomnia is usually caused by a life event, such as a stressful change in a person’s job, receiving bad news, or travel. Often acute insomnia resolves without any treatment.
A long-term pattern of difficulty sleeping. Insomnia is usually considered chronic if a person has trouble falling asleep or staying asleep at least three nights per week for three months or longer. Some people with chronic insomnia have a long-standing history of difficulty sleeping. Chronic insomnia has many causes.
Insomnia that occurs with another condition. Psychiatric symptoms — such as anxiety and depression — are known to be associated with changes in sleep. Certain medical conditions can either cause insomnia or make a person uncomfortable at night (as in the case of arthritis or back pain, which may make it hard to sleep.
Difficulty falling asleep at the beginning of the night.
The inability to stay asleep. People with maintenance insomnia wake up during the night and have difficulty returning to sleep.